1. Field of Invention
The invention relates to an image forming apparatus that forms an image by exposing a photosensitive member to a plurality of laser beams.
2. Description of Related Art
A laser printer is generally known as an electrophotographic image forming apparatus. In the laser printer, a uniformly charged surface of a photosensitive member is exposed to a beam of laser light emitted based on image data, to form an electrostatic latent image on the surface of the photosensitive member. The electrostatic latent image attaches toner thereto. An image is formed onto a sheet as the tone is transferred to the sheet.
As disclosed in, for example, U.S. Pat. No. 6,476,846, a plurality of laser beam emitting devices that emit laser beams are provided for a laser printer. The resolution of an image is improved by exposing the photosensitive member to the laser beams emitted from each of the plurality of laser beam emitting devices.
More specifically, as two laser beam emitting devices are controlled in parallel, the photosensitive member is scanned with the laser beams two lines at a time. Thus, line density is increased without reducing the rotating speed of the photosensitive member.
For example, an image of 1200 dpi resolution is formed with a laser printer having two laser beam emitting devices, by driving the photosensitive member at the same rotating speed as an image of 600 dpi resolution is formed with one laser beam emitting device.
The invention is directed to an image forming apparatus having a photosensitive member, an exposure device having a plurality of laser emitting elements that each irradiate a laser beam onto the photosensitive member to form an elactrostatic latent image on the photosensitive member, a developing device that supplies a developing agent to the electrostatic latent image to form a visible image, and a controller that controls the irradiation of the plurality of laser emitting elements. The controller includes a determining device that determines which laser emitting element from the plurality of laser emitting elements is closest to reaching its end of operating life and a restricting device that restricts the irradiation of the laser emitting element determined closest to reaching its end of operating life.